1. Field of the Invention
The present invention relates to the field of semiconductor processing. More specifically, the invention relates to an apparatus and method for carrying substrates through a processing system.
2. Background of the Related Art
In the semiconductor industry, there are two primary methods of moving substrates through a processing system. One traditional method uses a cluster tool arrangement shown in FIG. 1. A cluster tool platform 2 generally refers to a modular, multi-chamber, integrated processing system. It typically includes central wafer handling vacuum chambers 20, 32 and a number of peripheral processing chambers 24, 26, 28, and 36. Substrates such as wafers 22, typically stored in cassettes 10, are loaded and unloaded from load locks 12, 14 and processed under vacuum in various processing chambers without being exposed to ambient conditions. The transfer of the wafers for the processes is managed by a centralized robot 16 in a wafer handling vacuum chamber 20 or robot 30 in a second wafer handling vacuum chamber 32 which are maintained under vacuum conditions. A microprocessor controller 38 and associated software is provided to control processing and movement of wafers.
For relatively large substrates, such as glass substrates, ceramic plates, plastic sheets, and disks, a second method of moving substrates through a processing system, referred to as an inline system, is typically used. Glass substrates are used in the manufacture of flat panel displays, which are used as active matrix televisions, computer displays, liquid crystal display (LCD) panels, and other displays. A typical glass substrate has dimensions of about 550 mm by 650 mm and the trend is to increase the substrate size to about 650 mm by 830 mm and larger.
FIG. 2 is a schematic side view of a typical modular inline system 40. The processing system includes a serial arrangement of processing chambers 42, 44 disposed between a load chamber 46 and an unload chamber 48 on the ends of the series of processing chambers. An elevator 50 is disposed at an entry to the load chamber 46 and another elevator 52 is disposed at an exit from the unload chamber 48. The processing chambers, such as processing chamber 44, may include deposition chambers, such as chemical vapor deposition (CVD) chambers, physical vapor deposition (PVD) chambers, etch chambers, electroplating chambers, and other sputtering and processing chambers. A carrier return line 58 is disposed above the processing chambers and coupled to the elevators 50, 52. The various processing chambers are under vacuum or low pressure and are separated by one or more isolation valves 60, 62, 64, 66, 68 as shown in the schematic top view of the inline system in FIG. 3. Typically, multiple substrates 54, 56, 70, 72 are supported by a carrier 74, as shown in the schematic front view and side view of the carrier in FIGS. 4 and 5. The isolation valves seal the respective chambers from each other in a closed position and allow the substrates 54, 56 to be transferred through the valves to an adjacent station in an open position.
A carrier 74, shown in FIG. 2, is placed adjacent the elevator 50 where the substrates 54, 56, 70, 72 are manually loaded onto the carrier 74 at a receiving station 51. A door (not shown) to the elevator 50 opens and allows the carrier 74 to be placed within the elevator on a track (not shown). The temperature and pressure inside the elevator 50 is typically at ambient conditions. An isolation valve 60 opens and allows the carrier 74 to be moved on the track into a load chamber 46. The load chamber 46 is sealed and pumped down to a typical vacuum in the range of about 10 mTorr to about 50 mTorr for CVD processing and about 1 mTorr to about 5 mTorr for PVD processing. Another isolation valve 62 is opened and the carrier 74 is moved into a processing chamber 42, where the substrates are heated to a temperature suitable for processing. Another isolation valve 64 is opened and the carrier 74 is moved along the track into the processing chamber 44. If the processing chamber 44 is a sputtering process chamber, the chamber can include a plurality of targets 76, 78 that sputter material from the surface of the targets facing the substrates onto the substrates 54, 56, 70, 72 as the substrates move along the track adjacent each target. Each sputtering target is bombarded on the side facing the substrate with ionized gas atoms (ions) created between an anode (typically the target) and a cathode (typically the grounded chamber wall) and particles of the target are dislodged and directed toward the substrates for deposition on the substrates. Each target preferably has a magnet (not shown) disposed on the back side of the target away from the substrates to enhance the sputtering rate by generating magnetic field lines generally parallel to the face of the target, around which electrons are trapped in spinning orbits to increase the likelihood of a collision with, and ionization of, a gas atom for sputtering. The substrates 54, 56, 70, 72 are then moved to an unloading chamber 48 through isolation valve 66. Isolation valve 66 closes, thereby sealing the processing chamber 44 from the unload chamber 48. Isolation valve 68 opens and allows the carrier 74 to be removed from the unloading chamber 48 and the substrates 54, 56, 70, 72 are typically unloaded manually from the carrier. The substrates can also be detained in the unloading chamber to allow time for the substrates to cool. After the substrates have been unloaded, the carrier 74 enters the elevator 52, whereupon the elevator lifts the carrier 74 to the return line 58. A track system (not shown) in the return line 58 returns the carrier to the elevator 50, which lowers the carrier into position at the receiving station 51 on the other end of the processing system to receive a next batch of substrates to be processed.
While the inline system 40 is currently used for production, this type of inline system has several disadvantages. The carrier 74 undergoes thermal cycling as it is moved from a processing environment to an ambient environment in the elevators 50, 52 and carrier return line 58 and back into a processing environment. As a result, deposition material may peel off or be otherwise dislodged from the carrier 74 and cause unwanted particle inclusion on the substrates. Additionally, the track system can generate contaminants in operation that become attached to the carrier and can be brought into the processing chamber. The elevators and track system add a level of complexity to the system and maintenance is required of the various moving components to reduce breakdowns. Additionally, the carrier 74 will absorb oxygen in the ambient environment, which can increase the chamber pressure and cause contamination of deposited film layers when oxygen outgasses therefrom in the vacuum chamber. In addition to the thermal cycling of the carrier 74, the mean temperature of the carrier 74 typically rises as multiple sets of substrates are processed therewith at temperatures above ambient conditions. Most processes in processing chambers are temperature sensitive and typically a processing regime establishes a desired operating temperature to obtain consistent depositions. Consequently, heat transfer from the carrier 74 can affect the substrate and/or process and the films created at the beginning of production can vary compared to films created at the end of production with the increased mean temperature. Yet another challenge with the typical inline system is cross contamination between processes in adjacent processing chambers, especially those chambers using a reactive process. Reactive processing depends on two or more constituents in proper proportions. An influx of other materials from adjacent processing chambers can cause the reactive processing to be unstable and affect the deposition characteristics.
Therefore, there remains a need for an improved system and method for processing substrates, particularly relatively flat glass substrates.